This invention relates generally to a carrier box assembly for storing and transporting a plurality of thin flat objects including masks, displays, hard disks, silicon wafers and the like, and more particularly for the storage and transport of a plurality of semiconductor wafers.
Various prior art containers have been used in the electronics industry to transport masks, displays, disks, and wafers. The high value and fragile nature of such items requires a very reliable means for supporting them within the container. Many containers are configured specifically for the storage of semiconductor wafers because they are particularly valuable and fragile.
Semiconductor wafers are generally circular in shape and very thin. During the wafer manufacturing process, it is often necessary or desirable to move partially completed wafers from a first manufacturing facility to a second manufacturing facility for completion. This requires that the wafers be removed from the first production assembly, then packed and shipped to the second facility, where they are unloaded for further processing, without causing any damage to the wafer. Sources of damage include, but are not limited to, vibration, scraping, or impact during shipping, contamination of the wafer surface, or the destruction of printed circuitry by static electricity.
In the past, the handling of wafers by the edges has been preferred in order to prevent damage to, or contamination of, the surface of the wafer. Consequently, known semiconductor wafer carriers have generally stored wafers in stacked cassettes supporting the wafers only at the edges.
A continuing trend in the electronics industry is the ever increasing size, and decreasing thickness, of the wafers that must be stored and shipped. As the size and corresponding surface area of the disks increases, and as the thickness of the wafers decreases, new techniques must be found to protect them from damage. The use of rigid supports on the edges of the wafers (prevalent in prior containers) is not sufficiently effective in protecting these larger more delicate wafers. Furthermore, many prior shipping containers have not been well adapted for handling by robotic or automated machinery, thus requiring manual intervention at various stages for loading and unloading. In the processing of semiconductor wafers, there is an inverse relationship between chip yield and particle contamination. Every step requiring manual handling of the wafers increases contamination problems. Concern for particle contamination has increased as chip circuit geometries have decreased, because of the increased potential for contamination by ever smaller particles.
What is needed is a wafer carrier that fully supports the wafer in order to avoid damage to the wafer, that protects from the buildup of static charge, that is less expensive to manufacture than previous container designs, and that is configured to allow robotic handling of the carrier, and robotic manipulation of wafer.
Accordingly, the present invention is a shipping and storage container for storing and transporting a plurality of disc shaped objects, such as wafers and the like, while preferably protecting the items from vibration, abrasion, impact, particulation, static electricity, and outgassing. Although the embodiments described in this application are configured for holding wafers, the invention could be easily modified by one of ordinary skill for storing other materials including, hard disks, photomasks, liquid crystal displays, flat panel displays, and the like.
In its broadest sense, the invention comprises a separable base configured to hold a plurality of wafers stacked one on top of the other within a cylindrical storage area, and a cover configured to fit over portions of the base to enclose the stored wafers. More specifically, the carrier of the invention comprises a base with a deck having at least one wall defining the roughly cylindrical storage area, and a cover including a cylindrical recess or lid configured to fit over and around the vertical wall of the base.
In some embodiments, the base of the container includes four roughly identical walls with gaps between the ends of each wall. In other embodiments, these walls are hollow and may be used for holding desiccants, preferably in sealed packages. In various embodiments, the container of the invention also includes a number of useful features, including features used to allow handling of both the container and the wafers by robots or automated machinery, a tamperproof seal, a locking means to prevent accidental opening of the container, stiffening ridges, and data storage means for storing data regarding the contents of the containers. In one embodiment, the locking means is a locking assembly including at least one guide ridge and riser formed on the outer perimeter of one or more vertical walls of the base, and at least one corresponding locking tab formed on the inside surface of the cylindrical recess of the lid.
In use, the wafers are placed in vertical stacks within the cylindrical storage area defined by the vertical walls of the base, with lower wafers supporting the underside of upper wafers. Preferably, a protective material, including but not limited to cellulose, a flash-spun and heat-bonded high-density polyethylene (HDPE) fabric that is sold under the tradename a flash-spun and heat-bonded high-density polyethylene (HDPE) fabric that is sold under the tradename TYVEK, or foam discs, are placed between each pair of adjacent wafers. Furthermore, a layer of compressible material is preferably positioned between the top wafer and an underside of the lid. The compressible material fills any void left between the top of the stack and the underside of the lid. It is preferable to overfill the container with the compressive material, so that the overfill creates light compression on the wafers when the container cover is placed over the base, which tends to inhibit wafer movement inside the container, tending to reduce wafer damage.